The invention concerns a rotational pump with variable volume flow, comprising a pump housing having a suction connection and a pressure connection, an outer rotor with inner toothing which is rotatably disposed in the housing interior, and an inner rotor with outer toothing which is eccentrically disposed in the outer rotor, and which can be driven by a drive shaft which is disposed in the pump housing parallel to the axis of the outer rotor, wherein a rotatable adjusting ring, in which the outer rotor is eccentrically and rotatably disposed, is provided coaxially to the drive shaft for changing the volume flow in the pump housing.
DE 102 07 348 discloses rotational pumps, the theoretical supply volume of which can be changed by displacing the center of the outer rotor along a circle, the outer rotor being eccentrically and rotatably disposed in an adjusting ring which is rotatably disposed on the drive shaft in the pump housing, thereby permitting appropriate change of the position of both rotors relative to the suction and pressure connections. In order to avoid repetition, the full disclosure of this reference is hereby incorporated by reference.
It has turned out that when the volume flow is reduced through turning the adjusting ring, the required driving torque for the rotational pump does not change or only changes to a very small extent.
It has turned out to be disadvantageous that the suction stroke already starts before the suction chamber is connected to the suction connection thereby producing an underpressure in the suction chamber which demands drive energy and a drive torque. This underpressure is eliminated when the suction chamber is connected to the suction connection. This is effected in dependence on the position of the adjusting ring, at an earlier or later point in time of the suction stroke. The later that point in time, the larger the torque required to build up the underpressure. It has also turned out that the suction stroke may already start when the suction chamber is still connected to the pressure connection. The suction chamber could already be connected to the suction connection, thereby causing a hydraulic short-circuit.
It is the underlying purpose of the invention to provide a rotational pump of the above-mentioned type, wherein the driving torque is reduced for reduced volume flow.